There are a lot of variables.
Some people have trouble eating on chemotherapy drugs which makes them weaker. If you have a juicer, try a mineral rich combo of 3 celery sticks, a whole cucumber, and a small bunch of parsley. This neutral tasting combo has lots of minerals which chemotherapy seems to strip away.
Or chop up a stalk celery into small bits, dice up half a cucumber, mix in bits of fresh parsley and toss. Sliced a couple of cherry tomatoes for color and add to the mix. Top lightly with turmeric powder until you can barely see the color sprinkled. Add, if possible, a dash of coriander and cumin and serve.
The purpose is to refresh and revitalize. Make sure your hubby is not becoming dehydrated.
All things, including how exhausted he feels, will pass. Best wishes.